Williiamson's Weekly Notes - Sept 2 2009

One I saw this past August was almost pale enough to fool me into thinking I was seeing a small white, that is one of the so-called cabbage whites, which was tatty and worn. Calling myself an oaf and an idiot.

I quickly re-adjusted the record on my recording form with which I sample butterfly populations weekly, feeling rather silly that I'd made such an error. But the fact is, this little jewel of the chalk downs can easily be mistaken for another of the blue family, or at worst, a common old white, if the insect is faded.

Having not made this mistake before made me realise how fallible one may be. The problem was that I had not expected to see a chalkhill at that moment, and the place was swarming with whites. The photo, taken by Brian Henham on more or less the first day you could expect to see the rarity, July 24, is of a pristine male. Even so, it is pale, but the blue is not beyond the pale; it is still a bright blue and quite shiny as it fluttered about low down across the grass.

They never fly very high, always seem to be searching the chalk grassland within a few inches of the flower heads and the rabbit-grazed turf. I suppose the best places to find what many people suggest is one of the most iconic creatures of the Downs, is in East Sussex.

It likes Dover cliffs and the south side of the Isle of Wight as well as the Dorset chalk cliffs 'tis true. I also see it on Birdlip, overlooking the Severn valley in the Cotswolds.

There are colonies on the North Downs too. But the South Downs remains its main stronghold. One colony I have known for 40 years where I can expect to see 25 each August, is dependant on a patch of horse-shoe vetch which is only two yards square.

If that one patch of Hippocrepis was destroyed, by the action of, say, a wood camp fire, then that colony of butterflies would become extinct in the whole surrounding area of several square miles of downland.

Things in East Sussex are not quite so fragile, the caterpillars of this rarity having some quite large patches of the unusual little plant with the yellow flowers, to munch their way through. They will hardly ever eat anything else. Oh by the way, the female of the species is the colour of plain chocolate. Maybe you saw her as well. I do hope so.